1. Technical Field
This disclosure relates generally to the purification of fluids and more specifically to the desalination and purification of seawater or brackish water.
2. Related Art
Today's world has increasingly greater need for fresh, drinkable water. Current desertification is taking place much faster worldwide than historically, arising from the demands of increased populations. In addition, freshwater resources are being depleted, escalating the need for a new economically efficient way to produce potable water.
The abundant availability of seawater and development of new technologies for desalination of brine and brackish waters will be a potential solution to the pressing worldwide problem of limited freshwater supplies and sources, with major societal benefits and impacts. Thus there is global demand for desalination and fluid purification in general.
Desalination using membrane processes, which mainly rely upon reverse osmosis (RO), are presently the fastest growing technology, approximating around 22% of world desalination capacity. Reverse osmosis uses dynamic pressure to overcome the osmotic pressure of salt solutions, allowing water-selective permeation of salt-free water to migrate from the saline side of a membrane to the freshwater side. However, RO systems need high pressures (50 to 100 atm or 800 to 1500 psi) and extensive pre-treatment of seawater to allow sufficient permeation through the RO membrane, leading to a seawater conversion rate between about 35 to 50%. Furthermore, initial membrane costs and replacement issues lead to high capital investments and operating costs for RO systems.
Notwithstanding the advancement in water purification techniques, and in particular water desalination (purification) technology, the capital and operating costs of these processes remain significantly higher than the cost of retrieving natural fresh water and delivering it as potable fresh water. Water, in the United States, is typically priced for wholesale at $100 to $450 per acre-foot, depending on geographic location and proximity to freshwater sources. In California, the wholesale cost of freshwater is approximately $500 per acre-foot. Presently, the cost of desalination is in the range of $617 to $987 per acre-foot of desalinated water. Desalination of brackish water by RO processes, while cheaper, is still relatively expensive, ranging from $247 to $432 per acre-foot.
Consequently, a need remains for water purification processes that can operate with lower energy requirements, higher efficiency, and/or lower costs than the current state-of-the-art fluid purification processes.